Technical Field
The present invention relates to a color separating and combining prism incorporated in a projector, and in particular to a color separating and combining prism suitable for a projector employing a laser light source as an illumination light source, and a projector employing the same.
Background Art
Projectors employing an image display device such as a reflective liquid crystal panel or a digital micro-mirror device (DMD) have conventionally been known as apparatuses for projecting digital information such as video images contained in video recorders and documents and images contained in personal computers. Such a projector includes an illumination light source configured to radiate illumination light, an illumination optical system configured to guide the illumination light from the illumination light source to an image display device, and a projection optical system configured to guide projection light from the image display device to a projection lens.
The illumination light emanating from the illumination light source is guided and split into light rays of three colors of red, blue, and green through the illumination optical system, and guided to image display devices corresponding to the respective colors. The illumination light rays directed to the image display devices emanate from the image display devices as projection light rays, and the projection light rays are combined again, guided to the projection lens via the projection optical system, and projected onto a screen.
Furthermore, a color separating and combining prism is used to separate the illumination light and combine the projection light. That is, the color separating and combining prism is an optical member used for both of an optical system for guiding the illumination light and an optical system for guiding the projection light, and each constituted by a combination of a plurality of triangular prisms. Furthermore, dichroic films for separating and combining light are formed on predetermined surfaces, and the separation of the illumination light and the combination of the projection light rays are performed by reflecting a light ray having a predetermined wavelength on each dichroic film and allowing light rays having wavelengths other than the predetermined wavelength to pass through each dichroic film.
Conventionally used as the illumination light source are high-intensity xenon lamps, high-pressure mercury lamps, and the like. In recent years, light emitting diodes (LEDs) and laser light sources using semiconductor lasers have been in practical use for improvement in luminous efficiency and increase in luminous quantity. In particular, the development of blue laser light sources has led to the development of illumination light sources using light sources of three primary colors, which are blue laser light sources, green laser light sources, and red laser light sources.
With this background, there has already been proposed an image projection system provided with an illumination light source including laser light sources for the three respective primary colors of blue, green, and red, a color separating and combining prism, and a reflective image display device (see, for example, Patent Literature 1 listed below). Further, for large-screen projection of images, there has already been proposed an image projection system provided with a light source including a high-power xenon lamp, a color separating and combining prism, and a reflective image display device (see, for example, Patent Literature 2 listed below).